Telemetering system



Dec. 11, 1951 Filed Feb. 28,

E. HAYsLET ETAL 2,578,643

TELEMETERING SYSTEM 6 Sheets-Sheet l Dec. 1l, 1951 L. E. HAYsLETT ETAL 2,578,643

TELEMETERING SYSTEM Filed Feb. 28, 1947 6 Sheets-Sheet 2 me l@ z den Qms.'

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TELEMETERING SYSTEM Filed Feb. 28, 194'? 6 Sheets-Sheet 5 I @den fors lama?" @ys/eff Dec. ll, 1951 L. E. HAYSLETT ETAL 2,578,643

TELEMETERING SYSTEM Filed Feb. 28, 1947 6 Sheets-Sheet 4 SZK? 525 T 59 f/M/w// fahr/2595 Dec. 1l, 1951 L. E. HAYSLETT E'rAL 2,578,643

- TELEMETERING SYSTEM Filed Feb. 28, 1947 6 Sheets-Sheet 5 zz/elz 1o/1s.' 1 V lanzar @Hagysleff gZa/zcxl's/ZZ Scma'gi L. E. HAYSLETT TAL TELEMETERING SYSTEM 6 Sheets-Sheet 6 NWN [ama-r 6u.

Dec. 1l, 1951 Filed Feb. 28, 1947 `7f-UNITED sTATE's 'PATENT amsn orifice,

"rammen-:RING SYSTEM Lamar E. llayllett, Kenmore, and Francia M. Schmidt, North Tonawanda, N. Y., aaaignora to The Rudolph Wurlltaer Company, North Tonawanda, N. Y., a corporation oi Ohio application February 2s, 194i, sei-iai No. 731,410

This invention relates to remote indicating systems and particularly to radio telemetering sysilfiiis.'

- Certain telemetering systems are of the type in which a cyclically pulsed transmitter .sends out v spaced pulses of varying length thereby to transmit meter indications of varying values.` The pulses upon being received, are ampliiled and then limited to aconstant amplitude so that the length oi.' each pulse is the sole variable, thus eliminatl ing the detrimental effects of fading, interference, variations of equipment performance and other factors ordinarily affecting the accuracy of transmission and reception of the signal.

An object of the` present invention is to provide a system of the aforesaid character having incorporated therein various improvements which further insure the accuracy of operation and the reliability of the system in service. l

A More specically, the objects of this invention include the provision of better means of pickup from the transmitting instrument, more accurate pulsing means at the transmitting end, improved limiting means at the receiving end, more stable cyclic control o1 pulsing, multiple-channel pulsing, impedance matching or decoupling tubes between various functional circuits to prevent interaction, more stable pulse extinguishing circuits, improved stability with respect to supply voltage variations, temperature compensation features. and independent minimum and maximum pulse length adjustments.'

Various other objects, advantagesv and features'will become apparent from the following speciilcation when taken in connection with the accompanying drawings wherein a certain preferred embodiment is set forth for purposes of illustration.

In the drawings, wherein like reference numerals refer to like'parts throughout:

Fig. l is a block' diagram of -the transmitting and embodying the principles of the Fig. 3 is aschematic diagram of a portion'ot "the transmitting apparatus;

Qliigs. 4 A, 4B and 4C are oscilloscope patterns ofvarious control voltage variations under different operating conditions:

f i1-Fiss,... 5A, 5B ma 5c, taken meiner. constitute 11 Claims. (Cl. 177-351) l 2 a schematic diagram of the transmitting apparatus; and v Fig. 6 is a schematic diagram of the receiving equipment of the system.

The present invention is adapted for use in a system comprising a transmitting section. a receiving section and a radio link between said sections. 'Ihe transmitting section will be described first. This section is associated with one or more transmitting instruments or meters such as the aircraft instrument 8, Fig. 1. The reading or indication of each transmitting instrument usually determines the setting of an associated control potentiometer i0, Figs. 3 and 5B. In most instances it will be preferable to couple the potentiometer to the meter throughthe medium of a suitable torque amplifier or synchro arrangement 9, Fig. l. The transmitting section luncions to convert the various potentiometer settings into'radio signals in the form of spaced pulses having variable pulse lengths according to tlie values represented by the potentiometer settings.` Where the transmitting instrument is of such a' character that it produces its own output voltage, such voltage is used to control the formation of the data-transmissionl pulses in similar Y fashion, as will be described.

Referring to Fig. 1, a low-frequency oscillator i2 having a sine-wave output, as shown in Fig. 2A, of approximately 10 cycles per second controls the periodicity of the pulses transmitted by tne system. The oscillator I2 is coupled by an impedance matching tube I4 to a blocking oscillator I6, the latter oscillator being a device for producing extremely short, timed pulses as shown in Fig. 2C The effect which this has on the output voltage of tube i4 is shown in Fig. 2B. The timed pulses, Fig. 2C, are eiective to trigger a sawtooth generator i8 having an output as represented in Fig. 2D. A portion of this output is applied through an impedance matching tube 20 to one or more square wave generators as 22, there being one such generator for each telemetering channel. Another portion of the sawtooth output is utilized to time the operation of an extinguishing pulse generator 24 which produces extinguishing pulses as shown in Fig. 2E.

As will be explained in greater detail herein- Y after. each pulse of the square wave, Fig. 2F, is initiated at a selected time in the pulsing period corresponding to the indication of the transmitting .meter 8, and is terminated at the end of the period or cycle by an extinguishing pulse, Fig. 2E. A switch tube 26 controlled by generator 55 22 applies variable-length direct-current pulses,

interference at the receiving end. The output of the oscillator 30, after passing through the buffer 28, has a Waveform as shown in Fig. 2H, consisting of pulses of supersonic-frequency oscillationsv having constant periodicity and variable pulse length. These pulses are utilized to modulate a transmitter 32 which feeds an antenna 34 for transmitting the meter data by radio to the receiving apparatus. Preferably the transmitter 32 is of the frequency-modulated type and serves to transmit the signals in all telemetering channels on a common carrier frequency. A

Referring` now to Fig. A, the low-frequency oscillator I2 establishes the controlling frequency for all constant-periodicity functions of the transmitting section. Accuracy of data transmission dictates that this oscillator be unusually stable as to frequency regardlessof changes in the supply voltages and temperature. oscillator I2l againstsupply voltage fluctuations the anode of the tube 38 in the oscillator I2 is connected through a resistor 40 to the positive terminal of a voltage regulator tube 42, Fig. 5B, that is connected through certain resistors (to be described later) to a voltage source such as the generator 36, Fig. 5A. The voltage regulator 42 has a stabilizing effect upon the anode voltage supplied to the tube 38. Further stabilization with respect to supply voltage is accomplished by properly proportioning the relativevalues of the anode resistor 40, series grid resistors 44 and 46, and grid capacitor 48. Frequency stabilitywith respect to temperature is obtained by making the resistors 44 and 46 of conducting materials having different temperaturev coefficients. Resistor 44 is wound of wire having a very slight temperature coemcient ofresistance and may be considered to remain essentially constant in resistance. Re-v sistor 46 is of 'a carbon composition having a negative temperature coeillcient of resistance. 'I'he resistors 44 and 46 tend to produce shifts of oscillator frequency in opposite directions when there is a change in the temperature of the fre- To stabilize the capacitor 48 and tapped inductance 50. By selection of suitable relative values of resistors 44 and 46 the frequency of the oscillator I2 can be maintained essentially constant over a selected temperature range. v

An impedance matching or decoupling cathode follower tube I4 is interposed between the lowfrequency oscillator I2 and the blocking oscillator I6. The anode voltage for tube I4 `is obtained from a voltage regulator tube 18, Fig. 5A. Cathode resistor 54 normally biases the grid of tube I4 so that this tube operates on the negative portion of the grid voltage-plate current characteristic whereby the action of oscillator I6 does not reflect any change of load back to the oscillator I2. Voltage divider resistors 56 and 58 have relative values such as to produce the desired amplitude of low-frequency voltage applied to the grid of tube I4.

The blocking oscillator I6 includes a tube 68 and a transformer 62 and serves to produce extremely short, timed pulses of voltage for accurately controlling the firing of a gas tetrode or tube 80 and the cathode of tube 64.

thyratron 64, Fig. 5B,' in the sawtooth oscillator I 8. The anode-of tube 66, Fig. 5A, is connected through the primary 66 of transformer 62 and a decoupling resistor 68 to a voltage regulator tube '10 that is energized by the high-voltage source 36. The junction of primary 66 and resistor 68 is connected to ground through a resistor 12 and capacitor 14. The voltage appearing across the cathode resistor 54 of the cathode follower I4 is applied through a secondary 16 0f the transformer 62 and a capacitor 18 to the grid of the blocking oscillator tube 60, this grid being connected to ground through a resistor 80.

The connections of transformer 62 are so phased with respect to the grid and anode of tube 60 thatthe oscillator I6 tends to produce sustained oscillations. The oscillator circuit elements are so adjusted that the natural frequency of oscillator I6 is slightly lower than the controlling frequency-of the oscillator I2. When the sine-wave voltage applied to the grid of tube 68 attains a predetermined value, the tube 60 conducts, causing anode current to flow through the primary 66. The instant that anode current starts to flow in the primary 66, secondary 16 produces a high-voltage pulse to charge the capacitor 18. The phase of this charge is such as to drive the grid of tube 60 in the far negative region. thus effectively cutting off the flow of anode current. The circuit is so arranged that an extremely short-duration voltage pulse appears across the cathode resistor 82 of the oscillator I6. as indicated in Fig. 2C. As the charge on capacitor 18 leaks off, the grid potential of tube 68 ril. with the rise in the controlling sine-wave voltage until a condition of anode-cathode conduction again is established, whereupon the cycle is repeated.u Thus, timed pulses of extremely short duration are produced at regular intervals al determined by the periodicity of the lowfre quency oscillator I2.

The output pulses, Fig. 2C, of the blocking .oscillator I6 are utilized to control the firing of a thyratron 64, Fig. 5B. in the sawtooth generator circuit I8. This sawtooth generator is adapted to furnish sawtooth pulses of maximum linearity al indicated in Fig. 2D, the repetition rate of tin sawtooth pulses being controlled by the timing of pulses from the blocking oscillator I6. The values of capacitor 84 and resistor 86 are selected to allow operation on the steep portion of the charging characteristic of the timing capacitor 84. Anode voltage for the tube 64 is obtained through the resistor 86 from the voltage regulat' tube 42.

Tube 64 is ilred each time a pulse from the blocking oscillator I6 is impressed upon its control grid. Capacitor 84 thereupon discharg. through the tube 64. this portion` of the operation being represented by the vertical lines in the pattern of Fig. 2D. A sharp rise of potential therefore occurs across the cathode resistor 88 and Il communicated to the grid of an extinguisher tube in the extinguishing pulse generator 24. The function of this extinguisher will be explained more-fully hereinafter.' A capacitor 82 bypasses the resistor 88 to provide a low impedance path which facilitates the rapid discharge of timing capacitor 84. Voltage divider resistors 84 and 86 are selected forsuitably biasing the grid of Following the discharge of timing capacitor 84, upon termination of the ring pulse applied to the grid of tube 64, the capacitor-84 com- 5 mences to charge whereby a linearly increasing voltage appears on the anode of tube 64. This voltage is applied to thelgrid of the impedance matching tube 20 through a coupling capacitor l0. Tube 20 isarranged in a cathode follower circuit and functions as a low-impedance driver for furnishing sawtooth voltage to a number of squarev wave generators, such as 22, there being one such square wave generator for each telemetering channel that is to be .utilized in the system, In the illustrated embodiment it is assumed that there are three telemetering channels, respectively, including. the square wave generators 22, and |02. Gas tetrodes or thyratrons |04, |06 and |08 are included respectively in the generators 22, |00 and |02. The control grids of these thyratrons are connected respectively through decoupling resistors ||0, ||2 and ||4 to the cathode of tube 20, whereby interaction between the square wave generators is minimized. The control grid of tube |04 also is connected through a coupling resistor ||6 to the movable tap of the potentiometer I0, Figs. B and 3. It will be recalled that this potentiometer |0 has an operative connection through a servomechanism 9 or like device to a transmitting `instrument such as meter 8. Fig. 1. One end of the potentiometer I0 is grounded while the/other end is connected through a rheostat ||8 and fixed resistor |20 to the anode of the voltage regulator tube 42. which in turn is connected through the series resistors |22, |24 and |26 to the high-voltage source 36, Fig. 5A.

Anode voltage for the tubes |04, |06 and |08. Fig. 5B, is obtained from the voltage regulator tube 62, Fig. 5A, through the secondary |28 of a pulse transformer |30, Fig. 5B. The primary |32 of transformer |30 is arranged to be energized by the output of the extinguisher tube 90 as will be explained. Isolating resistors |34, |36 and |38 are incorporated in the anode circuits of the square wave generator tubes to minimize interaction.

A simplified schematic diagram showing the pertinent components of the transmitting chan- 'nel in which the square wave generator 22 is included is presented in Fig. 3. Omissions of circuit elements that are illustrated in Figs. 5B and 5C are indicated by dotted lines in Fig. 3. 'Ihe cathode of tube |04 is connected to the movable tap of a. potentiometer |40, one end of this potentiometer being connected through a resistor |42 to ground. The other end of the potentiometer is connected through a temperature-compensating combination of resistor |44 and resistor |46 to a junction |41 of resistors |22 and |24, Figs. 5A and 5B. This resistor pair serves to maintain operational stability with respect to temperature changes.

The general operation of the square wave generator 22 is such that a pulse is initiated by this generator when the combined potential of the sawtooth voltage and the steady voltage applied to the control grid of tube |04 attains the firing potential of this tube. The pulse thereafter is extinguished at a predetermined time whereupon the tube |04 is rendered nonconductive until its grid potential again is raised to the firing point. The potential E, Fig. 3, applied to the potentiometer |0 is adjusted by means of the rheostatv ||8, Fig. 5B, to give maximum pulse length for maximum setting of potentiometer I0, that is to say, for maximum reading of the transmitting instrument 8, Fig. l. The cathode potentiometer 40 is adJusted for a minimum pulse length corresponding annees 6 to minimum setting of the potentiometer I0. The direct-current voltage V, Fig. 3, which varies with the setting of 4potentiometer I0, is applied to the control grid of tube |04, while the sawtooth voltage from generator Il (through the medium of the impedance matching tube 20) is superimposed on this direct-current voltage. This causes the grid voltage of the tube |04 to vary as shown, for example, in Fig. 4A, which illustrates the operation for a minimum pulse length. Starting from the level V determined by the setting of the potentiometer I0, the combined potential rises until the sawtooth pulse is terminated, whereupon the cycle is repeated. As the grid voltage reaches the firing point, the tube |04 suddenly draws anode current. r

When each sawtooth pulse is terminated by the iiring of the tube 64, the tube 80, which normally is biased to cut off by proper selection of values of the voltage divider resistors |48 and |50 controlling the` cathode bias, suddenly becomes conductive and draws current through the primary |32 of the pulse transformer |30, discharging a capacitor |52. The resultant pulse in the secondary |28 of transformer |30 is of suiilcient negative value to cancel the positive voltage normally supplied to the anode of tube |04. The design of the transformer |30 and associated circuits is such as to maintain the negative pulse from secondary |28 for suiilcient duration to allow complete deionization of the tube |04 to take place, thereby extinguishing the pulse furnished by the square wave generator 22. The wave form of the square Wave generator output is as shown in Fig. 2F or in Fig. 3. After the grid l of tube has been returned to its normal cutoi potential when tube 64 ceases conducting, capacitor |52 is recharged from the positive voltage source 36 through a resistor |53, Fig. 5A.

The length L of the square wave pulse is dependent upon the setting of potentiometer |0. Thus, referring to Figs. 4A, 4B and 4C, an initially low setting of the potentiometer I0 lowers the starting level V of the sawtooth voltage variation so that a relatively long time is required to attain the ring voltage F of the tube. Under these conditions, the tube is fired late in the pulsing period and a pulse of short length L is produced. For a high setting of potentiometer |0 the starting voltage V is raised so that the firing voltage F is attained relatively early in the period, producing a pulse of greater length L, as shown in Fig. 4C. For an intermediate setting of potentiometer I0, an intermediate pulse length L is produced as indicated in Fig. 4B.

'Ihe pulse voltage that appears at the anode of tube |04 is reduced to a suitable level by voltage divider resistors |54 and |56, Fig.,5B, and is applied to the grid of the switch tube 26, Figs. 5C and 3, The voltage pulse furnished by the generator 22 to the grid of tube 26 is of negative sign, as indicated in Figs. 2F and 3. The tube 26 normally is maintained in a cut-off condition while the square wave generator tube 04 is conducting, by having its cathode suiiiciently positively biased by the voltage drop through divider resistors |58, |60 and |62. The anode of tube 26 is connected through a resistor |64 to the junction |65 of resistors |58 and |60. When the tube 26 is in its non-conducting state, the buffer 28 functions to pass the supersonic oscillations generated by the oscillator 30. This oscillator is of conventional design and is arranged so that a portion of its output voltage is fed through a' coupling capacitor |88 to the grid of the buffer tube |68. Self-bias is maintained on the tube |68 by alcathodev resistor |10. The anode of 'switch tube 28 is connected to the grid of buffer tube |68 through an isolating resistor |12. A parallel tuned circuit |14 is interposed between the resistors and |60 in the cathode circuit of tube |68. This tuned circuit is resonated at the supersonic frequency produced by oscillator 30 and minimizes the effects of stray signals from adjacent channels. The anode of tubel |68 is supplied with operating voltage by the regulator tube |18.

When the square pulse fromgenerator 22 is terminated, the grid of tube 26 rises in potential to a point where conduction takes place through this tube. Anode current drawn by the tube 26 produces a voltage drop in the resistor |64 which is effective to reduce the grid potential of tube |68 to the cut-off point, whereupon buffer 28 ceases passing the telemetering signal from the supersonic oscillator 30. When the square wave generator tube |04 again conducts and switch tube 26 is cut off, the grid potential of tube |68 rises for enabling the buffer 28 again to pass the supersonic signal. The output of switch tube 26' comprises positive pulses, Fig. 2G, each having a length commensurate with the length of the controlling pulse furnished by the square wave generator 22. As the tube 26 switches the conduction `of tube 28 on and off, it may be aptly termed a switch tube.V The signal passed by the buffer 28v comprises a pulsed supersonic-frequency signal as shown in Fig. 2H. This latter signal is utilized as a subcarrier for modulating the frequency-modulation transmitter of the system.

There has been described a channel of the telemetering systemincluding square wave generator 22, Figs. 1, 3 and 5B, switch tube 26, Fig. 5C, supersonic oscillator 30 and buffer 28. Other channels are of similar construction and arrangement; for instance, the channel which includes the square wave generator |02, Fig. 5B, may be controlled by a potentiometer |80 having an operative connection with a transmitting instrument similar to the meter 8, Fig. 1. A supersonic oscillator |82, Fig. 5C, having a frequency diferentfrom that of the supersonic oscillator 30, is provided for the channel under consideration. A switch tube |84 and buffer |85` function to initiate and terminate pulses of supersonic-frequency oscillations which are fed to the transmitter. All of the channels feed their output to a common output mixer tube |90, Fig. 5C, through coupling capacitors as |92 and isolating resistors as |94. The grid potentiometer |96 is provided to adjust the composite signal level for proper operation of tube |90. Output transformer |98 matches the output tube |90 to the transmission line leading to the modulator section of the transmitter. A balanced line has been found desirable for eliminating any possible stray pickup from nearby equipment. Cathode resistor 200 of tube |90 and bypass capacitor 20| produce the required operating bias for tube |90. The anode of tube |90 is connected through the primary of transformer |88 and an isolating resistor 202 to the high-voltage source 36, Fig. 5A. A capacitor 204 is provided to bypass the alternating-current component in the output of tube |80. With the exception of. the output mixer tube |80, all of the tubes illustrated in Fig. 5C are supplied with anode voltage from theregulator tube |16.

to control a telemetering channel by a transmit- ,n

There may be instances when it is desirable ting instrument which furnishes its own controlling voltage. Such an instrument would be a tachometer including a direct-current generator as 208, Fig. 5B, having an output voltage proportional to its rotational speed. In the system as illustrated herein the tachometer generator 208 is associated with the telemetering channel which includes the square wave generator |00. One terminal of the generator 208 is grounded and the other terminal is connected in series through resistor 2|8, potentiometer 2|2 and resistor 2|4 to ground. Maximum pulse length adjustment is effected by the potentiometer 2|2, the slider of which is connected through a resistor 2|6 to the control grid of tube |06, While minimum pulse length adjustment is'efiected by a potentiometer 2|8, the slider of which is connected to the cathode of tube |06. One side of potentiometer 2|8 is connected to ground through a resistor 220 while the other side thereof is connected through the temperature-compensating resistors 222 and 224 to the junction 226 between the resistors |24 and |26, Fig. 5A.

The output of square wave generator |00, Fig. 5B, through the medium of a switch tube 228, Fig. 5C, controls the passage of supersonic telemetering pulses from an oscillator 230 by a buffer 232 in substantially the same manner as previously described in connection with other telemetering channels. The output of the tachometercontrolled channel is fed to the mixer tube |90. It will be noted that the length of pulse furnished by this channel is determined not by the setting of an element such as a potentiometer, but by the magnitude of the controlling voltage developed by the tachometer generator 208. In its essential aspects, however, operation is no difierent from that described above.

A high degree of accuracy in the control of pulse length requires that compensation be provided'to offset changes in supply voltage. The use of voltage regulator tubes as 42, Fig. 5B, assists greatly to stabilize the Ivoltage. ever, because such devices do not operate perfectly, additional means are provided to obtain the results desired. Thus, in the case of the first telemetering channel described above, the string of resistors |42, |44 and |46 is returned to the junction |41 between resistors |22 and' |24 intermediate the unregulated voltage supply source 36 and the regulator tube 42. With this arrangement a change in supply voltage will affect the cathode potential of tube |04 to a greater extent than it will the grid potential of this tube. This serves to nullify the effect of such grid potential variation and also to compensate for the change of slope of the sawtooth voltage rise during the charging of timing capacitor 84. In the case of the tachometer-controlled telemetering channel, the connection of the resistor string 220, ZIB, 222 and 224 to the junction 225,4

tratesone channel only of the receiving equipment. As there shown. each channel is provided with a selective circuit 232 and an isolating resistor 224, which function to select av particular telemetering signal corresponding to such channel. The signal which is passed by the selective circuit has a wave form similar to that shown in Pig. 2H, comprising spaced pulses of supersonicfrequencyoscillations. An amplifier 236 amplifles this signal and feeds itto a rectifier 228 through a coupling capacitor. 240. An inductance 2.42 aHords a high impedance between the cathode of rectifier 228 and ground for the telemetering signal, yet provides a low-resistance directcurrent path to ground in order to maintain proper rectified direct-current voltage across the resistors' 244 and 246 in the output circuit of rectifier 236. Filter capacitors 248 and 250 aid to remove the supersonic-frequency component from the output of rectifier 256.

AJ voltage regulatortube 252 and regulating resistor 254 are arranged to supply a substantially constant direct-current voltage to a switch tube 256. The anode oftube 256 is connected directly to the anode of a control tube 256 and is also connected through 'a rheostat 260 and resistor 262 -to the anode of the regulator tube 252. The tube 256 is of the gas-filled regulator` type designed to regulate, for example, at 105 volts, whereas tube 252 regulates at a higher voltage, such as 150 volts. The cathode of tube 256 is connected through the receiving instrument, such as meter 264, to ground.,

The rectied and filtered direct-current output voltage from the rectifier 238 is applied to the grid of the control tube 256. This output voltage is in the form of a negative pulse when a telemetering signal pulse is being received by the channel. The grid of tube 258 is swung into the cut-off region by the pulse, thus stopping the ilow of anode current through this tube. Under these conditions, the tube 256 passes current at substantially constant -voltage through the meter 264. When the pulse is terminated, the tube 258 again conducts current, thereby reducing the potential across the tube 256 below the conducting value. 256 therefore ceases conducting and stops the ow of current through the meter 264.

The current which passes through the meter 264 is in the form of direct-current pulses having substantially constant amplitude and vari-` able pulse length. Preferably the meter 264 is a simple DArsonval type of instrument in which the pointer deilection is proportional to the average energy in the deilecting coil. Inasmuch as pulse length is the only variable. the meter deflection is a measure of the pulse length and therefore of the quantity represented thereby. The rheostaty 260 is adiusted so that the meter 264 has maximum reading when a pulse of maxilength is received. The meter has a calibrated zero position corresponding to minimum 10l tors are controlled by highly stabilized pulseinltiating and pulse-terminating means. This system will accommodate multiple channels without undue interference between channels.

-Impedance matching and decoupling tubes are .means comprising the control tube 256 and regulator tube 256. These and other features com- .bine to render a marked advancement in the art of telemetering.4

It is obvious that various changes may be made in the specific embodiments set forth for purposes of illustration without departing from the spirit of the invention. The invention is accordingly not to be limited to the specific embodiments shown and described, but only as indicated' in the following claims. The invention is hereby claimed as follows; 1. In a telemetering system lfor transmitting data by electrical pulses of variable length under the control of a transmitting instrument, a variable potential source controlled by said instrument, a sawtooth generator including a gas-filled electron tube and a timing capacitor having a discharge path through said tube when said tube is conductive, stabilized-frequency means for periodically rendering said tube conductive, a square wave generator arranged to be biased by said variable potential source, circuit Ameans for applying the output of said sawtooth generator to said square wave generator, said square wave generator being effective in response to a particular value of applied potential as determined by the bias voltage for initiating a control pulse, andan extinguishing pulse generator including a normally charged capacitor, an electron tube biased pulse length, and" all intermediate readings will be proportional to transmitted pulse' length.

It will be seen from the'foregoing that the invention provides aradio telemetering system having numerous advantageous features. The various pulsing devices at the transmitting end are highly accurate and dependable in operation. Stabilization against supply voltage fluctuations is provided wherever it is materially conducive to increased reliability. Temperature compensation is provided wherever changes in temperature are apt to have detrimental effects on the accuracy of ythe system. The square wave generaby said sawtooth generator and effective to discharge said normally charged capacitor concurrently with each discharge of said timing capacitor, and a pulse transformer having a primary arranged in the discharge path of said normally charged capacitorand a secondary arranged in the operating circuit of said square wave generator.

2. In a radio telemetering system, a transmitting instrument, a sawtooth generator, a stabilized-frequency oscillator controlling said sawtooth Vgenerator to iix the periodicity thereof at a substantially constant value, a thyratron having a predetermined firing voltage, means applying to said thyratron a voltage of. constant selected value as determined by the condition of said transmitting instrument together with a voltage of continually increasing value .derived from said sawtooth generator, an extinguishing pulsel generator controlled bysaid sawtooth generator for periodically interrupting the conduction of current by said thyratron, a telemetering signal generator, and electronic switching means including a first tube controlled by said thyratron whereby said first tube is cut olf when said thyratron is conducting, and a second tube so arranged in relation tosaid first tube and said signal generator that telemetering signal is passed a vtransmitting instrument, a pulse generator in- `:hitting instrument, said electron tube having a control grid connected to a movable contact of said first potentiometer, a rheostat in series with said first potentiometer, a regulated voltaf'e source for applying a substantially constant voltage across said rheostat and said first potentiometer, a se-ond potentiometer, said electron tube having a cathode connected to a movable contact of said second potentiometer, a source of operating voltage for said tube, resistance means connecting said second potentiometer to said operating voltage source, cyclic operating means for applying to said control grid a voltage having a sawtooth wave form whereby the total voltage applied to said control grid is the sum of the sawtooth voltage and the voltage derived' from said first potentiometer, and other cyclic operating means operating in timed relation with said first cyclic operating means to interrupt the supplv of operating voltage from said source thereof, said rheostat being adiustable to effect production by said pulse generator of a pulse having maximum predetermined length for maximum position of said transmitting instrument, said second potentiometer being adiustable tov effect production by said pulse generator of a pulse having minimum predetermined length for-minimum position of said transmitting instrument.

4. In a radio telemetering system for transmitting variable-length data pulses, a square wave generator including a thyratron, cyclically operating means for impressing periodically on the control grid of said thyratron4 a substantially linearly varying voltage. means for adiusting the quiescent potential of said grid to a selected value. means for adiusting the quiescent potential of the cathode of said thvratron to a selected value, and temperature-compensating means in circuit with said thyratron to maintain the difference in said quiescent potentials substantially constant irrespective of temperature changes within a given range.

5. In a radio telemetering svstem for transmitting data by pulses of variable length, a pulse generator including an electron tube having an anode. a cathode and a control grid. a source of operating voltage for said electron tube. a voltage regulator tube, a resistance element connecting said voltage regulator tube to said source, means connecting the grid of said electron tube to said voltage regulator tube. means anplving a continually varying voltage on said grid, said electron tube responding when the difference in potential between the grid and cathode thereof attains a predetermined value to initiate a pulse by said pulse generator, and means connecting the cathode of said electron tube to a point of intermediate resistance on said resistance element whereby fluctuations in the voltage supplied by said source produce compensating changes of potential at the grid and cathode of said electron tube.

6. In a radio telemetering system having means for transmitting pulsed radio signals and a receiver including means for demodulating such radio signals, means for amplifying the demodulated signals, means for rectifying the demodulated signals passed by said amplifying means. means including a voltage regulator tube for limiting the amplitude of rectified signal in the l2 output `of said rectifier, and a direct-current measuring instrument substantially in parallel with said regulator tube.

7. In a radio telemetering system having means for transmitting pulsed radio signals and a receiver including means for demodulating such radio signals, means for amplifying the demodulated signals, means for rectifying the demodulated signals passed by said amplifying means, a gas-filled regulator tube having a required minimum value of operating voltage, a regulated source of direct-current voltage, resistance means connecting said regulator tube to said voltage source, a direct-current meter connected in series with said regulator tube, and meansjflncluding an electron tube controlled by said rectifier and connected in circuit with said source and saidregulator tube for controlling the voltage across said regulator tube in response to the received signals. said electron tube being in parallel with said regulator tube and said meter.

8. 'I'he combination set forth in claim 7, wherein said electron tube is arranged to draw substantially no current from said source when a signal pulse of at least a predetermined minimum value is received, said electron tube being also effective in the absence of a signal pulse to draw suilicient current to reduce the voltage across said regulator tube below the required minimum value thereof.

9. A radio telemetering system comprising a plurality of square wave generators each including a thyratron, a sawtooth generator driving all said square wave generators, a stabilizedfrequency oscillator driving said sawtooth generator, individual adjusting devices for said square wave generators whereby the respective firing times of said thyratrons are selected separately, an extinguishing pulse generator operating in timed relation with said sawtooth generator for periodically and simultaneously extinguishing all said thyratrons, a plurality of telemetering signal generators of preselected different frequency each in a separate transmitting channel, a plurality of electronic switching devices respectively controlling said transmitting channels and arranged to respond respectively to said square wave generators, frequency-selective filters to prevent interaction between said transmitting channels, a radio transmitter, a common mixer stage for applying the outputs of all said channels as modulating signals to said transmitter, and a radio receiver having associated therewith a plurality of receiving channels corresponding respectively to said transmitting channels.

10. A radio telemetering system as set forth in claim 9, wherein each of said receiving channels comprises a frequency-selective filter, an amplifier, a rectifier, a limiter for controlling the amplitude of signal passed by said rectifier, and a direct-current meter in circuit with said limiter.

11, In a telemetering system having means for transmitting pulsed signals, receiving means including means to amplify the signals, means including a voltage regulator tube to limit the amplitude of the amplified signals, a second voltage regulator tube, and a measuring instrument in series with said second tube.

LAMAR E. HAYSLE'I'I. FRANCIS M. SCHMIDT.

(References on followingr page) REFERENCES CITED The following references are of record in the Number y, flle of this patent:

UNITED STATES PATENTS Name Date Helsing June 21, 1927 Schleicher July 3, 1934 Luck July 13, 1937 Luck Jan. 7, 1941 Johnannson Mar. 18, 1941 Kimball Apr. 21, 1942 Number 

